Since plants can not escape from applied pathogens because of their immobile nature, they must be able to defend themselves by direct or indirect response to the pathogenic challenge; and, most plants appear to undertake some general defense mechanism to protect themselves against infective pathogens, e.g., fungi, bacteria and virus.
In this connection, crude extract isolated from Phytolacca americana L. has been proved to inhibit in vivo synthesis of polypeptide(see: Owens, R. A. et al., Virology, 56:390-393 (1973)); and, said report has accelerated studies on the Phytolacca antiviral protein(hereinafter referred to as "PAP") isolated from Phytolacca americana L. Under the circumstances, PAPs such as PAP-I and PAP-II produced in spring and summer, respectively, and PAP-S produced from seed, have been discovered and isolated since the early 1970's(see: Irvin, J. D. et al., Arch. Biochem. Biophys., 169:522-528(1975); Irvin, J. D. et al., Arch. Biochem. Biophys., 200:418-425(1980)).
As a result of extensive studies on the PAP at the molecular level, it was determined that PAPs block the 60S ribosomal subunit of eucaryotic polypeptide synthesis machinery, which is a general phenomenon in light of the fact that other ribosome-inactivating proteins(RIPs) inactivate said subunit; and, structure and base sequence of PAP genome, a multigene family, have been elucidated(see: Lin, Q. et al., Plant Mol. Biol., 17:609-614(1991)). Further, it has been also reported that: PAP is synthesized and secreted from the cytosol and it is involved in the control of pathogenic virus; however, the detailed mechanism of virus inactivation has not been proved(see: Ready, M. P. et al., Proc. Natl. Acad. Sci., USA, 83:5053-5056(1986)).
On the other hand, many methods have been developed in attempts to prepare transgenic plants to confer resistance against viruses. These include methods of expression of genes encoding viral coat proteins(see: Nejidat, A. et al., Physiol. Plant., 80:662-668(1990)) and cucumber mosaic virus coat protein in tobacco plants(see: Cuozzo M. et al., Bio/Technology, 6:549-557(1988)). However, none of these attempts have revealed to be practicable in light of the level of protection against viruses and the spectrum of target viruses.
Accordingly, there is a need in the art for the development of a practicable transgenic plant to guarantee stable expression of variable antiviral proteins originated from eucaryotes as well as procaryotes and to confer broad viral resistance spectrum against diverse pathogenic viruses.
Under the circumstances, the present inventors designed a recombinant expression vector, which contains PIP gene isolated from cDNA library of Phytolacca insularis Nakai autogenous in Korea(see: U.S. Pat. No. 5,348,865); and, developed a transgenic potato plant transformed with the recombinant vector for Phytolacca insularis antiviral protein(hereinafter referred to as "PIP") comprising the PIP gene.